FBI Director Robert Mueller is sworn in on on Capitol Hill prior to testifying before the House Judiciary Committee. / J. Scott Applewhite, AP

by Kevin Johnson, USA TODAY

by Kevin Johnson, USA TODAY

WASHINGTON - FBI Director Robert Mueller staunchly defended the government's use of two secret surveillance programs Thursday, saying that the former defense contractor who recently disclosed details about the operations had caused "significant harm'' to the nation's security.

The director, in his first public remarks since the disclosures about the mass collection of U.S. citizens' telephone records and Internet monitoring of non-citizens, told the House Judiciary Committee that the former contractor, Edward Snowden, is the "subject of an ongoing criminal investigation.''

Mueller did not elaborate on the status of the inquiry, but he said that Snowden's actions had left the country "vulnerable.''

"One of the great vulnerabilities terrorists understand is their communications,'' Mueller told lawmakers, suggesting that enemies are now likely to alter their activities to avoid detection. "If we lose our ability get their communications, we are going to be exceptionally vulnerable.''

Had the telephone tracking program been in place prior to 9/11, the director said, intelligence and law enforcement officials would have had an "opportunity'' to derail the deadliest assault on U.S. soil.

Mueller referred to a post 9/11 inquiry, which found that one of the suicide hijackers, Khalid al-Mihdar, had made telephone calls from San Diego to an al-Qaeda safe house in Yemen that intelligence officials had identified prior to the attacks.

"The opportunity would have been there,'' Mueller said.

At the same time, according to numerous government reviews, U.S. authorities also failed to act on leads or develop additional information on al-Mihdar and fellow hijacker Nawaf al-Hazmi, who were known to have traveled to the U.S. more than a year before the Sept. 11, 2001, attacks.

Focusing primarily on the phone tracking program, which has collected tens of millions of call records on U.S. citizens, several lawmakers questioned the scope of the collection effort.

"The government's activity exceeds the authority that Congress provided,'' Rep. John Conyers, D-Mich., said, referring to the phone surveillance program as a "nationwide dragnet.''

Rep. Jerrold Nadler, D-N.Y., also questioned why the phone program had to remain secret since the first details about its existence were revealed years ago. Nadler referred to a 2006 USA TODAY report that disclosed a vast record collection effort.

The program "makes a mockery of the existing law,'' Nadler said.

The National Security Agency disclosures represented only one avenue of inquiry for lawmakers, who questioned the outgoing FBI director about the Boston Marathon bombings and its investigation into revelations that the Internal Revenue Service had targeted conservative groups for additional scrutiny.

Mueller defended the FBI's response to early information about one of the bombing suspects, Tamerlan Tsarnaev, provided by Russian officials nearly two years before the bombings.

The director said agents did an "excellent job'' in an investigation of Tsarnaev's activities but found no evidence of criminal activity at the time. Before closing the inquiry in late 2011, Mueller said Russian authorities did not respond to three separate requests for additional information about Tsarnaev, who was subsequently killed in an encounter with police in the days after the bombing. His brother, Dzhokhar Tsarnaev, has been charged in the April attack.

Mueller said the bureau was in the early stages of its IRS inquiry, although the director drew the ire of Rep. Jim Jordan, R-Ohio, who assailed Mueller for not offering more detail and not knowing who was leading the bureau's investigation.

"To the extent there is any evidence of criminal misconduct, we will follow the leads wherever (they) take us,'' Mueller said.